1. Field of the Invention
The present invention relates to a loop antenna, more particularly relates to a loop antenna able to obtain a reception performance of a circularly polarized wave equivalent to that of a patch antenna, by a simple configuration. The loop antenna of the present invention can be applied to an antenna system provided with an electronic apparatus connected with this antenna by a cable and to a vehicle mounting an antenna system able to obtain a reception performance of a circularly polarized wave equivalent to that of a patch antenna by installing this antenna system at a dielectric part of the vehicle.
2. Description of the Related Art
In the past, automobiles and other vehicles (moving bodies) have been equipped with antennas enabling the reception of radio waves even during movement. In general, the radio waves received by a vehicle have principally been the medium waves (MW) for AM radio and the very high frequency (VHF) or ultrahigh frequency (UHF) waves for FM radio or television.
However, in recent years, in addition to antennas receiving these radio waves, antennas for global positioning systems (GPS), antennas for receiving satellite waves of satellite digital broadcasts or their reradiated waves (gap filler waves), antennas for receiving waves for conversation over car phones, mobile phones, etc., and other antennas have become increasingly required for vehicles. Further, antennas for sending and receiving radio waves to and from parts of intelligent traffic systems (ITS) such as electronic toll collectors (automatic toll systems) for automatically collecting tolls on highways and toll roads and radio wave beacons of vehicle information communication systems (VICS) providing road traffic information have become necessary. Therefore, recent vehicles have had to mount antennas for receiving and sending a large number of types of radio waves (media).
Among the radio waves sent from and received by these moving bodies, the GPS waves, satellite digital broadcast waves, and electronic toll collector waves are a circularly polarized wave. Further, for conventional a circularly polarized wave antennas, patch antennas have usually been used. Among these patch antennas, ones comprised of ceramic or other dielectric boards on one surface of which planar ground conductors are laid and on the other surface of which radiating conductors are laid have often been employed. As this type of patch antenna, a low profile patch antenna for moving bodies used on the roofs of automobile and other moving bodies, that is, a low profile moving body use patch antennas, has been employed (for example, see Japanese Patent Publication (A) No. 2002-135045, FIG. 1 and FIG. 3).
However, the patch antenna disclosed in Japanese Patent Publication (A) No. 2002-135045 etc. is comprised of two types of dielectric boards superposed over each other and is formed with power parts passing through the boards, so there were the problems that the structure was complicated and the cost was high. As a result, the antenna system connecting a patch antenna disclosed in Japanese Patent Publication (A) No. 2002-135045 to an electronic apparatus by cables also became high in cost. Further, a vehicle mounting a patch antenna disclosed in Japanese Patent Publication (A) No. 2002-135045 etc. suffered from the problem of poor appearance due to the use of the patch antenna provided on the roof.